The present invention relates to a stump grinder attachment for a skid steer loader, which is controlled and driven by hydraulic fluid under pressure. The stump grinder has a rotary cutter wheel that is driven by a hydraulic motor, and the load on the cutter wheel causes the pressure in the motor to vary. The cross feed of the cutter wheel across a stump to be removed is controlled by a hydraulic cylinder, and the feed of this cylinder movement is variable as a function of the pressure in the cutter wheel drive motor.
Stump grinders are well known in the art, and all of them use a rotating cutter wheel that will engage a stump or other obstruction that is capable of being cut and then the wheel is swung laterally of the axis of the wheel in order to cut away or chip the stump the wheel is engaging. Many of these stump grinders mount on three point hitches and are driven from power takeoffs of tractors. Others are engine driven and are independent units that mount on wheels and can be transported from one place to another.
The ability to sense engine speed and control the function of a cross feed cylinder for a cutter wheel from a signal which is a function of engine speed of an engine driven wheel is disclosed in U.S. Pat. No. 5,588,474 as well as U.S. Pat. Nos. 6,014,996 and 5,845,689. All of these are related to an internal combustion engine that drives the cutter wheel and will drop in speed as the load on the cutter wheel increases.
The present invention relates to a stump grinder that has hydraulic drives and controls including a hydraulic drive motor for the cutter wheel, and various control cylinders for adjusting the depth, position, and lateral feed of the stump grinder wheel. The present invention includes a hydraulic circuit that controls the cross feed or swing cylinder which a pressure operated proportional valve that varies the rate of movement of the feed as a function of the pressure of the drive motor. It is a hydraulic pressure function, that controls the lateral feed of the cutter wheel, independent of governed engine speed.